tip4p + hybrid pair_style

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1

Hi LAMMPS users,

I am using ionic liquid + water ( tip4p/ice).

I’m unable to run the minimization and MD runs with mixed systems.

After few runs the pressure is increased vastly . I am attaching the data, para and input files…

spme important parts of files are.

while minimization, bond_coeff and angle_coeff of water are made some huge numbers, for MD runs, they are 0.0.

pair_style hybrid lj/cut/coul/long 12.0 lj/cut/coul/long/tip4p 13 14 15 24 0.1577 12.0
pair_modify tail yes
bond_style harmonic
angle_style harmonic
dihedral_style multi/harmonic
improper_style cvff
kspace_style pppm/tip4p 0.00001
special_bonds lj/coul 0.0 0.0 0.5

…

input file

units real
dimension 3
atom_style full

#read_restart r.rest
read_data data.bmim_bf4
include parm.bmim_bf4

neighbor 2 bin
neigh_modify delay 0 every 1 check yes page 100000 one 10000

timestep 1
run_style verlet

velocity all create 298.15 23482341 mom yes rot yes dist gaussian

fix 1 all shake 0.0001 10 2000 b 4 6 7 10 12 13 15 a 24
fix 2 all npt temp 298.15 298.15 1000.0 iso 0.0 0.0 2000.0

thermo_style multi
thermo 20
thermo_modify flush yes

dump 1 all custom 5000 dump.1npt id mol type xu yu zu
dump_modify 1 flush yes

restart 5000 rA.rest rB.rest
run 100000
#minimize 1e-10 1e-10 1000 1000
write_restart r.rest

thanks in advance.

karthik kumar

data.bmim_bf4 (2.4 MB)

parm.bmim_bf4 (9.3 KB)

in.bmim_bf4 (665 Bytes)

2

hi,

there are three problems with your input.
1) your box is far too large and your density is far too low
2) you don't need pair_style hybrid, just lj/cut/coul/long/tip4p will do.
    with a recent version, thanks to improvements from steve, it
    will be about 20% faster for the tip4p water, and if you use
    lj/cut/coul/long/tip4p/opt it will be even faster.
3) your equilibration schedule is not very effective.

so change your box boundaries to

  -32.50000 32.50000 xlo xhi
  -32.50000 32.50000 ylo yhi
  -32.50000 32.50000 zlo zhi

change your input to:

units real
dimension 3
atom_style full

read_data data.bmim_bf4-ak
include parm.bmim_bf4-ak

neighbor 2 bin
neigh_modify delay 0 every 1 check yes

timestep 2.0
run_style verlet

velocity all create 298.15 23482341 mom yes rot yes dist gaussian

thermo_style multi
thermo 500

fix 1 all shake 0.0001 10 2000 b 4 6 7 10 12 13 15 a 24
fix 3 all langevin 300.0 300.0 10.0 234537
fix 2 all nph iso 0.0 1000.0 200.0

dump 1 all custom 500 dump.equil-1.lammpstrj id mol type xu yu zu

restart 5000 rA.rest rB.rest
run 100000

undump 1
unfix 2 3

fix 2 all npt temp 298.15 298.15 200.0 iso 0.0 0.0 2000.0

dump 1 all custom 500 dump.equil-2.lammpstrj id mol type xu yu zu
write_restart r.rest
[[email protected]... tip4p] less data\. data\.bmim\_bf4 data\.bmim\_bf4\-ak data\.tip4p \[akohlmey@\.\.\.2072\.\.\. tip4p\] less data.bmim_bf4-ak
[[email protected]... tip4p]$ cat in.bmim_bf4-ak
units real
dimension 3
atom_style full

read_data data.bmim_bf4-ak
include parm.bmim_bf4-ak

neighbor 2 bin
neigh_modify delay 0 every 1 check yes

timestep 2.0
run_style verlet

velocity all create 298.15 23482341 mom yes rot yes dist gaussian

thermo_style multi
thermo 500

fix 1 all shake 0.0001 10 2000 b 4 6 7 10 12 13 15 a 24
fix 3 all langevin 300.0 300.0 10.0 234537
fix 2 all nph iso 0.0 1000.0 200.0

dump 1 all custom 500 dump.equil-1.lammpstrj id mol type xu yu zu

restart 5000 rA.rest rB.rest
run 100000

undump 1
unfix 2 3

fix 2 all npt temp 298.15 298.15 200.0 iso 0.0 0.0 2000.0

dump 1 all custom 500 dump.equil-2.lammpstrj id mol type xu yu zu
write_restart r.rest

and your parameters to match only the one pair style (mixing works for that).
and forget about minimization (only trouble for tip4p). and you should get to
an equilibrated restart with some patience.

axel